ABSTRACT The prevalence of Sleep Disordered Breathing (SDB) in patients with stable heart failure exceeds 50%, and usually goes unrecognized and untreated. Obstructive Sleep Apnea (OSA) has strong etiological relationships with obesity, aging, hypertension and diabetes, all of which are causes of chronic heart failure. In a large population based study, OSA was an independent risk factor for developing heart failure. Obesity, and aging, both on the rise in the general population, are risk factors for both OSA and heart failure. Therefore, it is likely that OSA is playing a significant role in the progression of cardiac dysfunction in patients with cardiovascular disease, obesity, or aging. OSA, an established cause of hypertension, promotes poor outcomes of hypertension, Coronary Artery Disease (CAD), and atrial and ventricular arrhythmia, all of which are causes of Acutely Decompensated Heart Failure (ADHF). Therefore, OSA may particularly be implicated in the acute decompensation of heart failure, a condition often triggered by atrial fibrillation, CAD or hypertension. Our preliminary data confirm that 62% of patients hospitalized with ADHF have unrecognized OSA;an even higher prevalence than the current estimates in patients with stable heart failure. Episodes of obstructive apnea produce intermittent hypoxia, increased sympathetic activity, and large negative intra-thoracic pressure swings, all of which are devastating perturbations in patients with deteriorating cardiac function and may lead to decompensated heart failure. There is strong evidence that treatment of OSA with Continuous Positive Airway pressure (CPAP) reduces fatal and non-fatal cardiovascular events. Additionally, in patients with OSA and underlying heart failure, CPAP improves ejection fraction, sympathetic activity, and functional status. Despite these findings, systematic approaches to identifying and treating new cases of OSA among patients hospitalized for ADHF or even patients with stable heart failure are not part of current management guidelines. An evaluation of a systematic diagnostic and therapeutic strategy for OSA in patients hospitalized with ADHF has not been undertaken to date. This proposed research will evaluate the impact of an approach of expedited inpatient identification and treatment of OSA on within hospital and 3 month post-discharge cardiac and functional outcomes, through a randomized trial. Patients with ADHF will undergo an in-hospital sleep study. Among patients with ADHF who are newly diagnosed with OSA, one group (n=85) will receive immediate treatment for OSA during their hospitalization while the other randomized group (n=85) will receive the current standard of care including outpatient diagnosis with in-lab sleep study and outpatient initiation of CPAP. The effect of this approach on patients'adherence to CPAP will also be evaluated. This proposed research will evaluate the impact of a systematic approach of inpatient identification and treatment of OSA in patients with Acutely Decompensated Heart Failure on within hospital and 3 month post- discharge cardiac and functional outcomes, through a randomized trial.